- Published: Saturday, 09 June 2012
- Written by Jon Chandler
- Hits: 4749
In appreciation for my help on the glass buster and other projects, my producer friend gave me a new iPad . Very generous and appreciated. This of course opens up a new world of applications and projects and a sudden interest in magazine articles about interfacing to the device.
In the current issue of Nuts&Volts, there is an article about using an iPxxx as a moisture meter for watering plants. It connects using only the audio port and uses no external power source. At a quick glance, I guessed they were using the microphone input as a ADC to measure moisture content but a longer look showed there was more to the system than that.
The moisture meter is based on a Project HiJack interface. This is a fascinating interface developed by Ye-Sheng Kuo, Thomas Schmid and Prabal Dutta at the University of Michigan and was presented at the ISLPED’10 Design Contest. The paper presented for the contest is very informative and can be found here. This incredibly cheap interface has two unique features that allow it to be used with many audio devices: 1) It derives power from an audio signal to power the required circuitry and 2) it used audio tones to create a bi-directional interface over the audio path. One of the driving goals to to create a low-cost interface that could be used with a huge range of sensors in developing countries. One of the awesome demonstration projects is a 2-lead EKG.Discuss this article in the forums (0 replies).